1. Field of the Invention
The present invention relates to a fuel injection valve controller apparatus for use in a gaseous fuel internal combustion engine and particularly, to a fuel injection valve controller apparatus suited for improving the starting performance of the engine at a lower temperature.
2. Description of the Invention
FIG. 10 is a longitudinal cross sectional view showing a conventional electromagnetic fuel injection valve (referred to as an "injection valve" hereinafter). A hollow sleeve 2 made of a magnetic material is fitted into a cylindrical housing 1 made of a similar magnetic material. The hollow sleeve 2 includes a stationary core 2a, a flange 2b, and a fuel inlet member 2c. An electromagnetic coil 4 (referred to as a "coil" hereinafter) is wound on a bobbin 3 and disposed in a space between the housing 1 and the stationary core 2a so that it surrounds the stationary core 2a. The stationary core 2a has a compression coil spring 5 therein for urging a plunger (movable core) 6, which is located opposite to one end of the hollow sleeve 2, in a direction to close the injection valve.
A valve seat 8 is provided in the tip of the housing 1, which slidably accommodates a needle valve 7 coupled to the movable core 6. The valve seat 8 is covered with a nozzle 9 and swagelocked together with the nozzle 9 to one (front) opening end of the housing 1. The flange 2b of the hollow sleeve 2 is also swagelocked to the other or rear opening end of the housing 1. The flange 2b is fixedly joined at top with a connector 10 made of an insulating material such as resin. The connector 10 has a terminal 10a therein electrically connected to the coil 4. The fuel inlet member 2c of the hollow sleeve 2 accommodates a strainer 12 which includes a filter net 11 therein. A fuel is admitted through the hollow sleeve 2 and flown to a space between the valve seat 8 and the needle valve 7.
In operation, energizing of the coil 4 through the terminal 10a causes the movable core 6 to be attracted toward the hollow sleeve 2 and the needle valve 7 to depart from the valve seat 8 as resisting against the yielding force of the compression coil spring 5. Accordingly, the fuel is ejected out from an injection aperture 13 provided in the front end of the valve seat 8. The energizing of the coil 4 or the injection of the fuel can be controlled depending on an operating condition of the engine.
For improving the response of the injection valve to the operating condition of the engine or making the injection valve compatible with injection of a large amount of fuel such as in a direct injection engine or a gaseous fuel internal combustion engine, it is essential to supply the coil 4 with a large quantity of electric current and thus increase the magnetic attraction of the stationary core 2a for valve opening. However, if such a higher current were fed throughout the energizing period, the temperature of the coil 4 may radically increase and extra scheme for radiating heat from relevant switching elements (or drivers) in a drive circuit for energizing the coil 4 will be needed and it will be rather difficult to realize in the industrial field.
For a countermeasure thereof, the coil current is provided of a higher intensity at the starting of valve opening and it is reduced to the revel of maintaining the valve opening after completion of the valve opening (when the needle valve has been lifted up). It is known that the coil current in the injection valve is varied depending on a change (increase) of the inductance due to amount of the movable core, that is, the coil current decreases as the needle valve is fully lifted up (as for example disclosed in Japanese Patent Publication No. SHO 62-4543). For example, a controller apparatus disclosed in Japanese Patent Laid-open Publication No. SHO 58-211538 provides detecting the completion of valve opening from a drop of the coil current corresponding to the end of lifting operation and then decreasing the coil current.
Fuel for automobile engines is commonly gasoline which, in some cases, is now replaced by gaseous fuel such as natural gas. Natural gas is stored under pressure in a container before used. For feeding the compressed natural gas (CNG) into an engine, such a type of the fuel injection valve for gasoline as described above may be employed.
The major disadvantage in use of the fuel injection valve for feeding compressed natural gas to the engine is as follows. As the natural gas is compressed by a compressor in which oil is applied for lubrication between its piston and cylinder wall, a portion of the oil and drops of water in the atmosphere are very likely to mix in the natural gas. Since only small amounts of the oil and water generally mixes in the fuel gas, they cause no trouble in the engine operation under normal conditions. However, water mixing in the fuel may be frozen at an extremely low temperature or in the winter, hence locking the needle valve to the valve seat or causing "cling up".
FIGS. 8A and 8B illustrate comparison of the valve opening period in the injection valve between without cling-up (FIG. 8A) and with cling-up (FIG. 8B), in which the waveform "a" is a valve opening pulse signal supplied to the coil 4, the waveform "b" is a current through the coil 4, and the waveform "c" is the lifting amount of the needle valve 7. At the time t0, the needle valve 7 starts lifting up and completes its lifting amount at t1 thus fully opening the injection valve. When a predetermined short length of time has elapsed after the full opening, the valve current is reduced to a lower level to maintain the valve opening. At the time t2, the pulse signal "a" is deenergized to start closing the valve. As clearly understood from the diagrams of comparison, the valve when cling up does not immediately responds to the rise of the pulse signal "a" and waits until the valve current is more increased. This causes the valve opening period AA to be shorter than in a normal operation, thus decreasing the injection of the fuel and impairing the performance at start up of the engine.